Abstract
Very little information is available with respect to dynamic aspects of oocyte development and to yolk composition of tuna species. Since histological approaches can offer considerable information about the ovarian development of fish, and because different cytochemical/immunohistochemical tests are suitable tools for proving the presence of different macromolecules in several organs/tissues/cells, they can be good biomarkers of the reproductive mechanism in fish. The present study investigates the presence and distribution of carbohydrates, proteins, glycoconjugates, lipids, calcium, iron and vitellogenin in the bluefin tuna, Thunnus thynnus oocytes during the synthesis of yolk (globules and granules) in the vitellogenic phase. During the initial vitellogenic phase, oocytes (diameter: 249 ± 21.87 mm) contain oil globules (or vacuoles) which consist exclusively of neutral lipids. During this phase very small yolk granules appear around the cytoplasm. Glycolipids, phospholipids, glycoproteins (Nacetyl- D-galactosamine –GalNAc– sugar residues), calcium, proteins rich in tyrosine, tryptophan, lysine, arginine, cysteine and cystine, as well as vitellogenin are the main constituents of the yolk granules and the follicular envelope of these real vitellogenic oocytes (diameter: 386 ± 79.04 mm). The intergranular cytoplasm of the vitellogenic oocytes also contain glycogen and glycoconjugates with Mannose –Man– and/or Glucose –Glc–; N-acetyl-D-galactosamine –GalNAc–; L-Fucose –Fuc– and Nacetyl- D-glucosamine –GlcNAc– and/or sialic acid –NANA– sugar residues. The zona radiata is mainly composed of proteins; in this cellular layer, scarce neutral glycoproteins and lipids (phospholipids/glycolipids) are also present.
Highlights
IntroducciónTuna is one of the most important groups of species in the fisheries industry because of the large size, unique taste and high market price of the fish
During the reproductive cycle of the bluefin tuna, T. thynnus L., vitellogenic oocytes were abundant in April and May
In fresh unfixed ovarian sections from criostat, these globules react with Oil Red O (ORO) and with Sudan Black B (SBB) and contain neutral lipids
Summary
IntroducciónTuna is one of the most important groups of species in the fisheries industry because of the large size, unique taste and high market price of the fish. The bluefin tuna, Thunnus thynnus L., is the largest species of tuna, reaching more than 3 m in total length, 500 Kg in body weight and having a high economic value. Thunnus thynnus is widely distributed throughout the world, with two reproductive areas: (1) the Mediterranean Sea within two different zones: around the Baleares Islands and in the South of the Tirrene Sea, between Sicily and Sardinia, where spawning occurs in June and July; and (2) the Gulf of Mexico and South of Florida, where spawning occurs in April and May. Thunnus thynnus thynnus is the Atlantic tuna and Thunnus thynnus orientalis is the Pacific tuna subspecies. African and European Atlantic tuna specimens migrate to the Mediterranean Sea (Davila, 1985)
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